Recently there is growing demand for fuel efficiency of vehicles. So, it is also desired to reduce the rotation torque of a tapered roller bearing used for supporting the rotation shaft of a transmission device and a axle differential device to be mounted on those vehicles.
As a method to reduce the rotation torque of a tapered roller bearing, there is the method of reducing rolling friction by providing a crowning to the rolling surface of a tapered roller and the raceway surface of an outer/inner ring.
As such a method, for example, Japanese Unexamined Patent Publication No. 2003-130059 proposes a method to reduce rotation torque by making an raceway surface in an arc crowning shape. Japanese Unexamined Patent Publication No. 2001-65574 proposes a method to change the rolling surface of a roller and the raceway surface tangent to the rolling surface to a crowning shape similar to a logarithmic curve.
The above-mentioned conventional arts improve the performance of tapered roller bearings by specifying the shapes for the crowning of the rolling surface or the raceway surface with values. However, there have been no attempts with regard to the crowning amount and to reduce the rotation torque of the tapered roller bearing by specifying the crowning amount.
The present invention was made to resolve the above problems and has the object of providing a tapered roller bearing to reduce rotation torque by providing the rolling surface of a tapered roller and the raceway surface of an outer/inner ring with a crowning and specifying the crowning amount.